Bulk amorphous refractory glasses based on the Ni(-Cu-)-Ti(-Zr)-Al alloy system

ABSTRACT

Bulk amorphous alloys based on quaternary Ni—Zr—Ti—Al alloy system, and the extension of this quaternary system to higher order alloys by the addition of one or more alloying elements, methods of casting such alloys, and articles made of such alloys are provided.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has certain rights in this invention pursuant toGrant No. DAAD 19-01-1-0525 awarded by the United States Army ResearchOffice.

This application claims the benefit of PCT/US2003/38683, filed Dec. 4,2003, published as PCT Publication No. WO2004/050930, and provisionalapplication No. 60/430,847 filed Dec. 4, 2002.

FIELD OF THE INVENTION

The present invention is directed to novel bulk solidifying amorphousalloy compositions, and more specifically to Ni-base bulk solidifyingamorphous alloy compositions.

BACKGROUND OF THE INVENTION

Amorphous alloys (or glassy alloys or metallic glass alloys) havetypically been prepared by rapid quenching a molten material from abovethe melt temperature to ambient temperature. Generally, cooling rates of10⁵° C./sec have been employed to achieve an amorphous structure inthese materials. However, at such high cooling rates, the heat cannot beextracted from thick sections of such materials, and, as such, thethickness of articles made from amorphous alloys has been limited totens of micrometers in at least in one dimension. This limitingdimension is generally referred to as the critical casting thickness andcan be related by heat-flow calculations to the cooling rate (orcritical cooling rate) required to form the amorphous phase.

This critical thickness (or critical cooling rate) can also be used as ameasure of the processability of an amorphous alloy (or glass formingability of an alloy). Until the early nineties, the processability ofamorphous alloys was quite limited and amorphous alloys were readilyavailable only in powder form or in very thin foils or strips withdimensions of less than 100 micrometers.

However, in the early nineties, a new class of amorphous alloys wasdeveloped that was based mostly on Zr and Ti alloy systems. It wasobserved that these families of alloys have much lower critical coolingrates of less than 10³° C./sec, and in some cases as low as 10° C./sec.Using these new alloys it was possible to form articles of amorphousalloys having critical casting thicknesses from about 1.0 mm to as largeas about 20 mm. As such, these alloys are readily cast and shaped intothree-dimensional objects using conventional methods such as metal moldcasting, die casting, and injection casting, and are generally referredto as bulk-solidifying amorphous alloys (bulk amorphous alloys or bulkglass forming alloys). Examples of such bulk amorphous alloys have beenfound in the Zr—Ti—Ni—Cu—Be, Zr—Ti—Ni—Cu—Al, Mg—Y—Ni—Cu, La—Ni—Cu—Al,and Fe-based alloy families. These amorphous alloys exhibit highstrength, a high elastic strain limit, high fracture toughness, andother useful mechanical properties, which are attractive for manyengineering applications.

Although a number of different bulk-solidifying amorphous alloyformulations have been disclosed in the past, it is still desirable toseek alloy compositions with higher temperature stability, bettercorrosion resistance, higher processability, higher and modulus, higherspecific strength and modulus, and lower raw material cost. Accordingly,a need exists to develop novel compositions of bulk solidifyingamorphous alloys which will provide improvements in these properties andcharacteristics.

SUMMARY OF THE INVENTION

The present invention is directed to Ni-base bulk-solidifying amorphousalloys, and particularly to alloys based on the Ni—Zr—Ti—Al quaternarysystem.

In one exemplary embodiment, the Ni—Zr—Ti—Al quaternary system isextended to higher alloys by adding one or more alloying elements.

In another embodiment, the invention is directed to methods of castingthese alloys into three-dimensional bulk objects, while retaining asubstantially amorphous atomic structure. In such an embodiment, theterm three dimensional refers to an object having dimensions of least0.5 mm in each dimension, and preferably 1.0 mm in each dimension. Theterm “substantially” as used herein in reference to the amorphous metalalloy means that the metal alloys are at least fifty percent amorphousby volume. Preferably the metal alloy is at least ninety-five percentamorphous, and most preferably about one hundred percent amorphous byvolume.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1a is a graphical depiction of x-ray diffraction scans of anexemplary bulk amorphous alloy; and

FIG. 1b is a graphical depiction of differential scanning calorimetry(DSC) plots of an exemplary bulk amorphous alloy.

DESCRIPTION OF THE INVENTION

The present invention is directed to bulk-solidifying amorphous alloysbased on a Ni—Zr—Ti—Al quaternary system, and the extension of thisternary system to higher order alloys by the addition of one or morealloying elements. These alloys are referred to as Ni-based alloysherein.

Although a number of different Ni—Zr—Ti—Al combinations may be utilizedin the Ni-based alloys of the current invention, a range of Ni contentfrom about 27 to 58 atomic percentage, a range of Ti content from about8 to 22 atomic percentage, a range of Zr content from about 13 to about37 atomic percent, and a range of Al content from about 5 to about 17atomic percent are preferably utilized.

To increase the ease of casting such alloys into larger bulk objects,and for increased processability, a formulation having a range of Nicontent from about 37 to 49 atomic percentage, a range of Ti contentfrom about 13 to 20 atomic percentage, a range of Zr content from about25 to about 32 atomic percent, and a range of Al content from about 8 toabout 12 atomic percent is preferred. Still more preferable is aNi-based alloy having a range of Ni content from about 39 to 47 atomicpercentage, a range of Ti content from about 15 to 18 atomic percentage,a range of Zr content from about 27 to about 30 atomic percent, and arange of Al content from about 9 to about 11 atomic percent.

Although only combinations of Ni, Ti, Zr and Al have been discussed thusfar, it should be understood that other elements can be added to improvethe ease of casting the Ni-based alloys of the invention into largerbulk objects or to increase the processability of the alloys. Additionalalloying elements of potential interest are Cu, Co, Fe, and Mn, whichcan each be used as fractional replacements for Ni; Hf, Nb, Ta, V, Cr,Mo and W, which can be used as fractional replacements for Zr and Ti;and Si, Sn, Ge, B, and Sb, which can be used as fractional replacementsfor Al.

It should be understood that the addition of the above mentionedadditive alloying elements may have a varying degree of effectivenessfor improving the processability of the Ni-base alloys in the spectrumof compositional ranges described above and below, and that this shouldnot be taken as a limitation of the current invention.

Given the above discussion, in general, the Ni-base alloys of thecurrent invention can be expressed by the following general formula(where a, b, c are in atomic percentages and x, y, z are in fractions ofwhole):(Ni_(1-x)TM_(x))_(a)((Ti,Zr)_(1-y)ETM_(y))_(b)(Al_(1-z)AM_(z))_(c),where a is in the range of from 27 to 58, b in the range of 21 to 59, cis in the range of 5 to 17 in atomic percentages; ETM is an earlytransition metal selected from the group of Hf; Nb, Ta, V, Cr, Mo, andW, and preferably from the group of Hf and Nb; TM is a transition metalselected from the group of Mn, Fe, Co, and Cu, and preferably from thegroup of Cu and Co; and AM is an additive material selected from thegroup of Si, Sn, Ge, B, and Sb, and preferably from the group of Si andSn. In such an embodiment the following constraints are given for the x,y and z fraction: x is less than 0.3, y is less than 0.3, z is less than0.3, and the sum of x, y and z is less than about 0.5, and under thefurther constraint that the content of Ti content is more than 8 atomicpercent and Zr content is more than 13 atomic percent.

Preferably, the Ni-based alloys of the current invention are given bythe formula:(Ni_(1-x)TM_(x))_(a)((Ti,Zr)_(1-y)ETM_(y))_(b)(Al_(1-z)AM_(z))_(c),where a is in the range of from 37 to 49, b in the range of 38 to 52, cis in the range of 8 to 12 in atomic percentages; ETM is an earlytransition metal selected from the group of Hf, Nb, Ta, V, Cr, Mo, andW, and preferably from the group of Hf and Nb; TM is a transition metalselected from the group of Mn, Fe, Co, and Cu, and preferably from thegroup of Cu and Co; and AM is an additive material selected from thegroup of Si, Sn, Ge, B, and Sb, and preferably from the group of Si andSn. In such an embodiment the following constraints are given for the x,y and z fraction: x is less than 0.2, y is less than 0.2, z is less than0.2, and the sum of x, y and z is less than about 0.3, and under thefurther constraint that the content of Ti content is more than 13 atomicpercent and Zr content is more than 25 atomic percent.

Still more preferably, the Ni-based alloys of the current invention aregiven by the formula:(Ni_(1-x)TM_(x))_(a)((Ti,Zr)_(1-y)ETM_(y))_(b)(Al_(1-z)AM_(z))_(c),where a is in the range of from 39 to 47, b in the range of 42 to 48, cis in the range of 9 to 11 in atomic percentages; ETM is an earlytransition metal selected from the group of Hf, Nb, Ta, V, Cr, Mo, and Wand preferably from the group of Hf and Nb; TM is a transition metalselected from the group of Mn, Fe, Co, and Cu and preferably from thegroup of Cu and Co; and AM is an additive material selected from thegroup of Si, Sn, Ge, B, and Sb and preferably from the group of Si andSn. In such an embodiment the following constraints are given for the x,y and z fraction: x is less than 0.1, y is less than 0.1, z is less than0.1, and the sum of x, y and z is less than about 0.2 and under thefurther constraint that the content of Ti content is more than 15 atomicpercent and Zr content is more than 27 atomic percent.

For increased processability, the above mentioned alloys are preferablyselected to have five or more elemental components. It should beunderstood that the addition of the above mentioned additive alloyingelements may have a varying degree of effectiveness for improving theprocessability within the spectrum of the alloy compositional rangesdescribed above and below, and that this should not be taken as alimitation of the current invention.

Other alloying elements can also be added, generally without anysignificant effect on processability when their total amount is limitedto less than 2%. However, a higher amount of other elements can cause adegradation in the processability of the alloys, an d in particular whencompared to the processability of the exemplary alloy compositionsdescribed below. In limited and specific cases, the addition of otheralloying elements may improve the processability of alloy compositionswith marginal critical casting thicknesses of less than 1.0 mm. Itshould be understood that such alloy compositions are also included inthe current invention.

Exemplary embodiments of the Ni-based alloys in accordance with theinvention are described in the following:

In one exemplary embodiment of the invention the Ni-based alloys havethe following general formula:Ni_(100-a-b-c)Ti_(a)Zr_(b)Al_(c),where 8<a<22, 13<b<37, 5<c<17.

In one preferred embodiment of the invention the Ni-based alloys havethe following general formulaNi_(100-a-b-c)Ti_(a)Zr_(b)Al_(c),where 13<a<20, 25<b<32, 8<c<12.

The most preferred embodiment of the ternary Ni-based alloys have thefollowing general formulaNi_(100-a-b-c)Ti_(a)Zr_(b)Al_(c),where 15<a<18, 27<b<30, 9<c<11.

Although higher order combinations of Ni-base alloys with five or moreelemental components can be utilized in the current invention, in oneparticularly exemplary embodiment of the invention, the five componentalloy system comprises combinations of Ni—Ti—Zr—Al—Cu, where the Nicontent is from about 27 to 47 atomic percentage, the Ti content is fromabout 8 to 22 atomic percentage, the Zr content is from about 13 toabout 37 atomic percent, the Cu content is up to 17 atomic percent, andthe Al content is from about 5 to about 17 atomic percent.

To increase the ease of casting such alloys into larger bulk objects,and for increased processability, a formulation having a range of Nicontent from about 37 to 44 atomic percentage, a range of Ti contentfrom about 13 to 20 atomic percentage, a range of Zr content from about25 to about 32 atomic percent, a range of Cu content from about 2 to 8atomic percentage, and a range of Al content from about 8 to about 12atomic percent is preferred. Still more preferable is a Ni-based alloyhaving a range of Ni content from about 39 to 42 atomic percentage, arange of Ti content from about 15 to 18 atomic percentage, a range of Zrcontent from about 27 to about 30 atomic percent, a range of Cu contentfrom about 3 to about 7 atomic percent and a range of Al content fromabout 9 to about 11 atomic percent.

It should be understood that other elements can be added to improve theease of casting the five component Ni-based alloys of the invention intolarger bulk objects or to increase the processability of the alloys.Additional alloying elements of potential interest are Co, Fe, and Mn,which can each be used as fractional replacements for Ni and Cu moiety;Hf; Nb, Ta, V, Cr, Mo and W, which can be used as fractionalreplacements for Zr and Ti moiety; and Si, Sn, Ge, B, and Sb, which canbe used as fractional replacements for Al.

It should be understood that the addition of the above mentionedadditive alloying elements may have a varying degree of effectivenessfor improving the processability of the Ni-base alloys in the spectrumof compositional ranges described above and below, and that this shouldnot be taken as a limitation of the current invention.

Given the above discussion, in general, the Ni-base alloys based on theNi—T—Zr—Cu—Al combination can be expressed by the following generalformula (where a, b, c are in atomic percentages and x, y, z are infractions of whole):((Ni Cu)_(1-x)TM_(x))_(a)((Ti,Zr)_(1-y)ETM_(y))_(b)(Al_(1-z)AM_(z))_(c),where a is in the range of from 27 to 58, b in the range of 21 to 59, cis in the range of 5 to 17 in atomic percentages; ETM is an earlytransition metal selected from the group of Hf, Nb, Ta, V, Cr, Mo, andW, and preferably from the group of Hf and Nb; TM is a transition metalselected from the group of Mn, Fe, and Co, and preferably Co; and AM isan additive material selected from the group of Si, Sn, Ge, B, and Sb,and preferably from the group of Si and Sn. In such an embodiment thefollowing constraints are given for the x, y and z fraction: x is lessthan 0.3, y is less than 0.3, z is less than 0.3, and the sum of x, yand z is less than about 0.5, and under the further constraint that thecontent of Ti content is more than 8 atomic percent, Zr content is morethan 13 atomic percent and Cu content is less than 17 atomic percent.

Preferably, the Ni-based alloys of the current invention are given bythe formula:((Ni,Cu)_(1-x)TM_(x))_(a)((Ti,Zr)_(1-y)ETM_(y))_(b)(Al_(1-z)AM_(z))_(c),where a is in the range of from 37 to 49, b in the range of 38 to 52, cis in the range of 8 to 12 in atomic percentages; ETM is an earlytransition metal selected from the group of Hf, Nb, Ta, V, Cr, Mo, andW, and preferably from the group of Hf and Nb; TM is a transition metalselected from the group of Mn, Fe, and Co, and preferably Co; and AM isan additive material selected from the group of Si, Sn, Ge, B, and Sb,and preferably from the group of Si and Sn. In such an embodiment thefollowing constraints are given for the x, y and z fraction: x is lessthan 0.2, y is less than 0.2, z is less than 0.2, and the sum of x, yand z is less than about 0.3, and under the further constraint that thecontent of Ti content is more than 13 atomic percent, Zr content is morethan 25 atomic percent, and Cu content is from about 2 to 8 atomicpercentage

Still more preferably, the Ni-based alloys of the current invention aregiven by the formula:((Ni,Cu)_(1-x)TM_(x))_(a)((Ti,Zr)_(1-y)ETM_(y))_(b)(Al_(1-z)AM_(z))_(c),where a is in the range of from 39 to 47, bin the range of 42 to 48, cis in the range of 9 to 11 in atomic percentages; ETM is an earlytransition metal selected from the group of Hf, Nb, Ta, V, Cr, Mo, andW, and preferably from the group of Hf and Nb; TM is a transition metalselected from the group of Mn, Fe, and Co, and preferably Co; and AM isan additive material selected from the group of Si, Sn, Ge, B, and Sb,and preferably from the group of Si and Sn. In such an embodiment thefollowing constraints are given for the x, y and z fraction: x is lessthan 0.1, y is less than 0.1, z is less than 0.1, and the sum of x, yand z is less than about 0.2, and under the further constraint that thecontent of Ti content is more than 15 atomic percent, Zr content is morethan 27 atomic percent, and Cu content is from about 3 to 7 atomicpercentage.

Other alloying elements can also be added, generally without anysignificant effect on processability when their total amount is limitedto less than 2%. However, a higher amount of other elements can cause adegradation in the processability of the alloys, an particularly whencompared to the processability of the exemplary alloy compositionsdescribed below. In limited and specific cases, the addition of otheralloying elements may improve the processability of alloy compositionswith marginal critical casting thicknesses of less than 1.0 mm. Itshould be understood that such alloy compositions are also included inthe current invention.

Exemplary embodiments of the Ni-based alloys in accordance with theinvention are described in the following examples:

In one exemplary embodiment of the invention the Ni-based alloys havethe following general formulaNi_(100-a-b-c-d)Ti_(a)Zr_(b)Al_(c)Cu_(d),where 8<a<22, 13<b<37, 5<c<17, and 0<d<17.

In one preferred embodiment of the invention the Ni-based alloys havethe following general formulaNi_(100-a-b-c-d)Ti_(a)Zr_(b)Al_(c)Cu_(d),where 13<a<20, 25<b<32, 8<c<12, and 2<d<8.

The most preferred embodiment of the pentiary Ni-base alloys have thefollowing general formulaNi_(100-a-b-c-d)Ti_(a)Zr_(b)Al_(c)Cu_(d),where 15<a<18, 27<b<30, 9<c<11, and 3<d<7.

Alloys with these general formulations have been cast directly from themelt into copper molds to form fully amorphous strips or rods ofthickness up to 6 mm. Examples of these bulk metallic glass formingalloys are given in Table 1, below.

TABLE 1 Critical Casting Alloy Composition (at %) Thickness (mm)Ni₄₅Ti₂₀Zr₂₅Al₁₀ 2 Ni₄₅Ti₂₀Zr₂₀Al₁₀Hf₅ 2Ni_(32.5)Ti_(12.5)Zr_(32.5)Al₁₀Cu_(12.5) 3 Ni₃₃Ti₁₃Zr₃₂Al₁₀Cu₁₂ 3Ni₃₇Ti₁₈Zr₂₉Al₁₀Cu₆ 3 Ni₄₀Ti₁₆Zr₂₃Al₁₀Cu₆Hf₅ 3 Ni₄₀Ti₁₆Zr₂₈Al₁₁Cu₅ 3Ni₄₀Ti₁₈Zr₂₆Al₁₀Cu₆ 3 Ni₃₅Ti₁₄Zr₃₁Al₁₀Cu₁₀ 4 Ni₃₇Ti₁₅Zr₃₀Al₁₀Cu₈ 4Ni₃₉Ti₁₈Zr₂₉Al₁₀Cu₄ 4 Ni_(39.6)Ti_(15.84)Zr_(27.72)Al_(9.9)Cu_(5.94)Si₁4 Ni₄₀Ti₁₆Zr₂₈Al₁₀Cu₆ 4 Ni_(40.5)Ti_(16.2)Zr_(28.3)Al₁₀Cu₅ 4Ni₄₁Ti₁₆Zr₂₈Al₁₀Cu₅ 4 Ni_(41.5)Ti₁₈Zr₂₇Al₁₀Cu_(3.5) 4Ni₄₂Ti₁₅Zr₂₈Al₁₀Cu₅ 4 Ni₄₃Ti₁₉Zr₂₆Al₁₀Cu₂ 4Ni_(38.7)Ti_(17.2)Zr_(29.8)Al₁₀Cu_(4.3) 5 Ni₃₉Ti₁₇Zr₂₉Al₁₀Cu₅ 5Ni₃₉Ti_(17.5)Zr_(28.5)Al₁₀Cu₅ 5 Ni_(39.6)Ti_(16.9)Zr_(29.1)Al₁₀Cu_(4.4)5 Ni₄₀Ti₁₆Zr₂₉Al₁₀Cu₅ 5 Ni₄₀Ti₁₇Zr₂₈Al₁₀Cu₅ 5 Ni₄₀Ti₁₇Zr₂₉Al₁₀Cu₄ 5Ni₄₀Ti_(17.5)Zr_(28.5)Al₁₀Cu₄ 5 Ni_(40.5)Ti_(16.5)Zr₂₈Al₁₀Cu₅ 5Ni_(40.5)Ti_(16.75)Zr_(28.25)Al₁₀Cu_(4.5) 5Ni_(40.5)Ti₁₇Zr_(28.5)Al₁₀Cu₄ 5 Ni₄₁Ti₁₇Zr₂₈Al₁₀Cu₄ 5Ni₄₁Ti_(17.5)Zr_(27.5)Al₁₀Cu₄ 5 Ni_(41.5)Ti_(17.5)Zr_(27.5)Al₁₀Cu_(3.5)5 Ni₃₉Ti₁₆Zr₂₉Al₁₀Cu₆ 6 Ni₃₉Ti_(16.5)Zr_(28.5)Al₁₀Cu₆ 6Ni_(39.8)Ti_(15.92)Zr_(27.86)Al_(9.95)Cu_(5.97)Si_(0.5) 6Ni_(39.8)Ti_(16.42)Zr_(28.36)Al_(9.95)Cu_(5.97)Si_(0.5) 6Ni_(39.8)Ti_(16.42)Zr_(28.36)Al_(9.95)Cu_(4.97)Ge₁ 6Ni₄₀Ti_(16.5)Zr_(28.5)Al₁₀Cu₅ 6Ni₄₀Ti_(16.5)Zr_(28.5)Al₁₀Cu_(4.5)Si_(0.5) 6Ni₄₀Ti₁₇Zr_(28.5)Al₁₀Cu_(4.5) 6 Ni₄₀Ti₁₇Zr₂₈Al₁₀Cu_(4.5)Si_(0.5) 6Ni_(40.25)Ti_(16.5)Zr_(28.5)Al₁₀Cu_(4.75) 6Ni_(40.3)Ti_(16.42)Zr_(28.35)Al_(9.95)Cu_(4.48)Si_(0.5) 6Ni_(40.4)Ti_(16.46)Zr_(28.43)Al_(9.97)Cu_(4.49)Si_(0.3) 6Ni_(40.5)Ti_(16.25)Zr_(28.75)Al₁₀Cu_(4.5) 6Ni_(40.5)Ti_(16.5)Zr_(28.5)Al₁₀Cu_(4.5) 6Ni_(40.5)Ti_(16.5)Zr_(28.5)Al₁₀Cu₄Sn₁ 6 Ni_(40.5)Ti₁₇Zr₂₈Al₁₀Cu_(4.5) 6Ni_(40.75)Ti_(16.5)Zr_(28.5)Al₁₀Cu_(4.25) 6Ni₄₁Ti_(16.5)Zr_(28.5)Al₁₀Cu₄ 6 Ni₄₁Ti₁₇Zr₂₈Al₁₀Cu₅ 6

The above table gives the maximum thickness for which fully amorphousstrips are obtained by metal mold casting using this exemplaryformulation. Evidence of the amorphous nature of the cast strips can bedetermined by x-ray diffraction spectra. Typical x-ray diffractionspectra for fully amorphous alloy strips is provided in FIG. 1a.

The invention is also directed to methods of casting these alloys intothree-dimensional bulk objects, while retaining a substantiallyamorphous atomic structure. In such an embodiment, the term threedimensional refers to an object having dimensions of least 0.5 mm ineach dimension. The term “substantially” as used herein in reference tothe amorphous alloy (or glassy alloy) means that the metal alloys are atleast fifty percent amorphous by volume. Preferably the metal alloy isat least ninety-five percent amorphous and most preferably about onehundred percent amorphous by volume.

In general, crystalline precipitates in bulk amorphous alloys are highlydetrimental to their properties, especially to the toughness andstrength, and as such generally preferred to a minimum volume fractionpossible. However, there are cases in which, ductile crystalline phasesprecipitate in-situ during the processing of bulk amorphous alloysforming a mixture of amorphous and crystalline phases, which are indeedbeneficial to the properties of bulk amorphous alloys especially to thetoughness and ductility. These cases of mixed-phase alloys, where suchbeneficial precipitates co-exist with amorphous phase are also includedin the current invention. In one preferred embodiment of the invention,the precipitating crystalline phases have body-centered cubiccrystalline structure.

Another measurement of the processability of amorphous alloys can bedescribed by defining a ΔTsc (super-cooled liquid region), which is arelative measure of the stability of the viscous liquid regime of thealloy above the glass transition. ΔTsc is defined as the differencebetween Tx, the onset temperature of crystallization, and Tsc, the onsettemperature of the super-cooled liquid region. These values can beconveniently determined using standard calorimetric techniques such asDSC measurements at 20° C./min. For the purposes of this disclosure, Tg,Tsc and Tx are determined from standard DSC (Differential ScanningCalorimetry) scans at 20° C./min. Tg is defined as the onset temperatureof glass transition, Tsc is defined as the onset temperature ofsuper-cooled liquid region, and Tx is defined as the onset temperatureof crystallization. Other heating rates such as 40° C./min, or 10°C./min can also be utilized while the basic physics of this techniqueare still valid. All the temperature units are in ° C.

Generally, a larger ΔTsc is associated with a lower critical coolingrate, though a significant amount of scatter exists at ΔTsc values ofmore than 40° C. Bulk-solidifying amorphous alloys with a ΔTsc of morethan 40° C., and preferably more than 60° C., and still more preferablya ΔTsc of 90° C. and more are very desirable because of the relativeease of fabrication.

Typical examples of DSC scans for fully amorphous strips are given inFIG. 1b. The vertical arrows in FIG. 1b indicate the location of theobserved glass transition and the observed crystallization temperatureof an exemplary alloy which was cast up to 5 mm thick amorphous strips.Further, Table 2, below gives the measured glass transition temperatureand crystallization temperatures obtained for the alloys usingDifferential Scanning Calorimetry scans at heating rates of 10-20 K/s.The difference between Tg and Tx, ΔT=Tx−Tg, is measure of thetemperature range over which the supercooled liquid is stable againstcrystallization when the glass is heated above Tg. The value of ΔT is ameasure of the “processability” of the amorphous material uponsubsequent heating. Values of this parameter are also given in Table 2,as reported values ranging up to ΔT˜50 K are observed.

TABLE 2 Critical Casting Tg Tx ΔT Alloy Composition (Atomic %) Thickness(K) (K) (K) Ni₄₅Ti₂₀Zr₃₅ 0.5 725 752 27 Ni₄₅Ti₂₀Zr₂₇Al₈ <0.5 761 802 41Ni₄₅Ti₂₀Zr₂₅Al₁₀ 2 773 818 45 Ni₄₅Ti₂₀Zr₂₃Al₁₂ <0.5 783 832 49Ni₄₀Ti₁₆Zr₂₈Al₁₀Cu₆ 3.5 766 803 42 Ni₄₀Ti₁₇Zr₂₈Al₁₀Cu₅ 4 762 808 46Ni_(40.5)Ti_(16.5)Zr₂₈Al₁₀Cu₅ 4 764 809 45 Ni₄₀Ti_(16.5)Zr_(28.5)Al₁₀Cu₅5 763 809 46 Ni_(39.8)Ti_(15.92)Zr_(27.86)Al_(9.95)Cu_(5.97)Si_(0.5) 5768 815 47

To assess the strength and elastic properties of these new metallicglasses, we have carried out measurements of the Vickers Hardness andcompression tests. Typical data are shown in Table 3, below. Typicalvalues range from V.H.=700 to 900. Based on this data, and usingempirical scaling rules, one can estimate the yield strength, Y.S. ofthese materials. Here we have used the approximate formula:Y.S.=(V.H.)×3where the approximate yield strength is given in MPa and the VickersHardness is given in Kg/mm². The yield strength values can be as high as2.5 GPa and among the largest values of Y.S. of any bulk amorphousalloys reported to date.

Table 3 also gives values for Poisson ratio (ν), shear modulus (μ) andYoung's modulus (E) of exemplary alloys. These elastic properties datawere obtained by measuring the sound propagation velocities of planewaves (longitudinal and transverse, C₁ and C_(s), respectively) in thealloys, then using the following relations (valid for isotropicmaterials such as amorphous alloys):ν=(2−x)/(2−2x)=Poisson's ratio, where x=(C₁/C_(s))²μ=ρ*C_(s) ²=shear modulus, where ρ is densityE=μ*2(1+ν)=Young's modulusAs can be seen from the data, the Young's modulus for these new bulkamorphous alloys is relatively large, i.e., these are relatively “stiff”bulk amorphous alloys.

TABLE 3 Yield Shear Young Vickers Strength Poisson's Modulus ModulusAlloy Composition (Atomic %) Hardness (GPa) ratio (GPa) (GPa)Ni₄₅Ti₂₀Zr₂₅Al₁₀ 791 2.37 0.36 42.7 116 Ni₄₀Ti₁₆Zr₂₈Al₁₀Cu₆ 780 2.20.361 41.5 113 Ni₄₀Ti₁₇Zr₂₈Al₁₀Cu₅ 862 2.3 0.348 50.1 135.1Ni_(40.5)Ti_(16.5)Zr₂₈Al₁₀Cu₅ 787 2.36 0.36 42.5 115.5Ni₄₀Ti_(16.5)Zr_(28.5)Al₁₀Cu₅ 800 2.4 0.355 45.6 123.7Ni_(39.8)Ti_(15.92)Zr_(27.86)Al_(9.95)Cu_(5.97)Si_(0.5) 829 2.49 0.3643.5 118.2

In sum, the inventors discovered a new family of bulk metallic glassforming alloys having exceedingly high values of hardness, elasticmodulus (E), yield strength, and glass transition temperature, Tg. Thevalues of these characteristic properties are among the highest reportedfor any known metallic alloys which form bulk metallic glass. Here,“bulk” is taken to mean that the alloys have a critical castingthickness of the order of 0.5 mm or more. The properties of these newalloys make them ideal candidates for many engineering applications.

Although specific embodiments are disclosed herein, it is expected thatpersons skilled in the art can and will design alternative Ni-basedalloys that are within the scope of the following claims eitherliterally or under the Doctrine of Equivalents.

What is claimed is:
 1. A glass forming alloy consisting of an alloyhaving a composition given by: Ni_(100-a-b-c-d)Ti_(a)Zr_(b)Al_(c)Cu_(d), where 15<a<18, 27<b<30, 9<c<11, 3<d<7.
 2. Theglass forming alloy described in claim 1 wherein the alloy has a ΔTsc ofmore than 40° C.
 3. The glass forming alloy described in claim 1 whereinthe alloy has a Vickers hardness greater than 700 Kg/mm².
 4. The glassforming alloy described in claim 1 wherein the alloy has a yieldstrength of greater than 2.5 GPa.
 5. The glass forming alloy describedin claim 1 wherein the alloy has a Young's modulus of greater than 140GPa.
 6. The glass forming alloy described in claim 1 wherein the alloyhas a ratio of glass transition temperature to liquidus temperature ofaround 0.6 or more.
 7. The glass forming alloy described in claim 1wherein the alloy is substantially amorphous.
 8. The glass forming alloydescribed in claim 1 wherein the alloy contains a ductile crystallinephase precipitate.
 9. The glass forming alloy described in claim 1wherein the critical cooling rate is less than about 1,000° C./sec. 10.A glass forming alloy consisting of an alloy having a composition givenby:Ni_(100-a-b-c-d)Ti_(a)Zr_(b)Al_(c)CU_(d)Ni_(100-a-b-c-d)Ti_(a)Zr_(b)Al_(c)Cu_(d),where 15<a<18, 27<b<30, 9<c<11, 3<d<7, and a+b+c+d is in the range offrom 58 to
 61. 11. The glass forming alloy described in claim 10 whereinthe critical cooling rate is less than about 1,000° C./sec.
 12. A threedimensional article made from the alloy of claim 1 having an amorphousphase.
 13. A three dimensional article made from the alloy of claim 10having an amorphous phase.
 14. The glass forming alloy of claim 1 havinga composition of Ni₄₀Ti₁₆Zr₂₈Al₁₀Cu₆.
 15. The glass forming alloy ofclaim 1 having a composition of Ni₄₀Ti₁₇Zr₂₈Al₁₀Cu₅.
 16. A Ni-basedglass forming alloy consisting of Ni, Ti, Zr, and Al, wherein a criticalcasting thickness of the glass forming alloy is 2 mm or more, wherein acontent of Al is about 8 to about 17 atomic percent, wherein thecritical casting thickness is a maximum thickness for which fullyamorphous strips are obtained by metal mold casting.
 17. The Ni-basedglass forming alloy of claim 16, wherein the atomic percent of Al isgreater than 8 and less than
 12. 18. The Ni-based glass forming alloy ofclaim 16, wherein a content of Zr is about 25 to about 37 atomicpercent.
 19. The Ni-based glass forming alloy of claim 16, wherein acontent of Zr is 29 to about 37 atomic percent, wherein the Ni-basedglass forming alloy is a bulk amorphous alloy.
 20. A Ni-based glassforming alloy consisting of Ni, Ti, Zr, Al, TM, ETM and AM, given by theformula:(Ni_(1-x)TM_(x))_(a)((TiZr)_(1-y)ETM_(y))_(b)(Al_(1-z)AM_(z))_(c)wherein a is in the range of from 37-49, b is in the range of 38 to 52,c is in the range of 8 to 12 atomic percentages; wherein ETM is a metalselected from the group consisting of Hf, Nb, Ta, V, Cr, Mo, and W, TMis a transition metal selected from the group of Cu, Co, Fe, Mn, and AMis an additive material selected from the group of Si, Sn, Ge, B, Sb andwherein x is less than 0.2, y is less than 0.2, z is less than about 0.3and the content of Ti is more than 13 atomic percent and the Zr contentis more than 30 atomic percent and wherein a critical casting thicknessof the glass forming alloy is 0.5 mm or more.